Field of the Invention
The present invention relates to a manufacturing method of a honeycomb structure, and more particularly, it relates to a manufacturing method of a honeycomb structure to be manufactured by laying a firing setter under an unfired honeycomb formed body and firing the honeycomb formed body.
Description of the Related Art
Heretofore, a honeycomb structures made of ceramics have been used in broad use applications of a car exhaust gas purifying catalyst carrier, a diesel particulate removing filter, a heat reservoir for a burning device and the like. The honeycomb structure made of ceramics (hereinafter referred to simply as “the honeycomb structure”) is manufactured by preparing a forming material (a kneaded material), extruding the forming material into a desirable honeycomb shape by use of an extruder, and firing a rawly cut, dried and finish-cut honeycomb formed body at a high temperature through a firing step.
In the above firing step, the honeycomb formed body is mounted on a shelf plate in a state where one formed body end face is directed downward, and the honeycomb formed body is thrown together with the shelf plate into a firing furnace. At this time, for the purpose of preventing the honeycomb formed body from adhering to the shelf plate, a firing base plate called “a setter” is interposed between the shelf plate and the honeycomb formed body, to prevent the honeycomb formed body from coming in contact directly with the shelf plate. As the setter, for example, there is used a disc-like member obtained by cutting the honeycomb structure of the fired honeycomb formed body into a predetermined thickness. Furthermore, for the purpose of preventing the disadvantage that the setter is cracked due to its repeated use, there might be used a setter called “a pressed setter” obtained by press-molding a ceramics material and firing this material. These setters are generically defined as “a firing setter” in the present specification. Furthermore, a body subjected to extrusion prior to the firing is called “the honeycomb formed body” and the body fired through the firing step is called “the honeycomb structure”.
The extruded honeycomb formed body is introduced into the firing furnace set at a predetermined firing temperature and the firing step is carried out. At this time, firing shrinkage is generated along a longitudinal direction (an axial direction) of the honeycomb formed body and a direction perpendicular to the longitudinal direction of cells. Therefore, in a case where the honeycomb formed body is mounted on the firing setter, a shift occurs between an upper surface of the firing setter (which corresponds to a honeycomb mounting surface) and a formed body end face of the honeycomb formed body due to the firing shrinkage during the firing, and defects such as “cell deformation” in the formed body and face and “partition wall crack” in which the partition walls are divided might occur.
Furthermore, when the formed body end face is stuck on the honeycomb mounting surface, the firing shrinkage is not uniformly performed and a shape of the formed body end face might be deformed. As a result, in the case of a round pillar-shaped honeycomb structure, there occurs a “roundness” defect indicating that the shape of the formed body end face does not become round. The above defects due to the use of the firing setter become remarkable especially in a case where a partition wall thickness of the partition walls defining a plurality of cells is small or in a case of firing a large honeycomb formed body having a large honeycomb diameter.
Especially, in the case of firing the honeycomb formed body having a small partition wall thickness, “a raw setter” is used which is obtained by cutting an unfired honeycomb formed body made of the same material as in the honeycomb formed body. The raw setter is made of the same material and therefore generates the same degree of firing shrinkage as in the honeycomb formed body, thereby avoiding the above problem that the honeycomb formed body is stuck on the honeycomb mounting surface of the raw setter, or the like. As a result, it is possible to suppress the possibility that the partition wall crack causes the roundness defect.
On the other hand, a setter (a firing base plate) has already been suggested which is capable of inhibiting the honeycomb formed body from being stuck on the honeycomb mounting surface of the firing setter which comes in contact with the honeycomb formed body and which is capable of minimizing a contact area (e.g., see Patent Document 1 or 2). In such a setter, the honeycomb mounting surface (the setter-upper surface) is flattened or is constituted of a curved surface rising from a side edge portion toward a central portion, thereby avoiding generation of resistance of firing shrinkage or binding between the honeycomb formed body and the firing setter in the firing step, and it is possible to manufacture the honeycomb structure without causing the cell deformation, the partition wall crack, and the like.
[Patent Document 1] JP-A-2000-274954
[Patent Document 2] JP-A-2003-82403